Error on hikashop > hikainvoce interaction

Hi,

First, please note that we are not linked to the development of this extension.
It was developed by a third party developer years ago. And we reference it on our integration page, like we reference many other extensions made to be compatible with HikaShop, most of them not developed or supported by us.
So, we won't be able to help you directly with any issue you might find in that extension.

If I read about this extension on the Joomla Extensions Directory ( extensions.joomla.org/extension/hikainvoices/ ) it says that it is compatible with Joomla 3 and Joomla 4, but it doesn't mention anything about Joomla 5. Also, the latest version was released more than 2 years ago, well before Joomla 5 was released. So I'm surprised you were even able to install it on your website, if you're on Joomla 5.

This extension is developed by the company Edwin2Win, which mainly works on the extension JMS Multisites:
www.jms2win.com/
As per its page on the JED ( extensions.joomla.org/extension/multi-sites/ ) this extension is still maintained and compatible with Joomla 5. They also provide more contact details on their contact page include their phone number:
www.hikainvoices.com/contact-us.html
Since it's been one month they didn't answer your ticket, I would first recommend phoning them to check what's going on.

But I suppose they won't be able to come up with a Joomla 5 support in a few days or weeks. So it's likely you'll have to ask for a refund through PayPal.